1. Field of the Invention
This invention relates to a pinhole inspection device, and, more specifically, to a pinhole inspection device for making a pass/fail quality inspection of a sample under inspection, such as a meter dial plate having a pattern area and a background area, wherein pinholes may exist in the background area.
2. Description of the Related Art
A known pinhole inspection device is disclosed in Japanese Unexamined Patent Publication No. 4-2952.
The above publication discloses a pinhole inspection device that performs a pass/fail discrimination for a sample under Inspection based only on pinhole size.
In a product, such as a meter dial plate, which consist of a pattern area including, for example, numerals, and a background area where no indicia are provided, if there is a pinhole in the background area that is so small that it is not recognized as a pinhole by an observer, the meter dial plate can be properly classified as good. To date, a general visual inspection is considered the best for performing such pass/fail discriminations.
For the reason discussed above, it is desirable that a pinhole inspection device be used to perform pass/fail discrimination for products, such as meter dial plates, wherein the inspection device has a function that approximates a visual pass/fail discrimination as closely as possible.
However, because the pass/fail discrimination by visual inspection and a pass/fail discrimination based on pinhole size have completely different criteria for pass and fail, it is not desirable to use the above-described known pinhole inspection device in a pass/fail discrimination of products, such as meter dial plates.